Interference-reducing means for radio receiving apparatus



Sept. 11 1928. r 683,916 #2. H. RANGER INTERFERENCE NEDUCING MEANS FOR RADIO RECEIVING APPARATUS Filed Dec. 18. 1922 Fig.5

Snoeutoz K. H RANGE R Patented Sept. 11, 1928 UNITED STATES PATENT OFFICE.

RICHARD HOWLAND RANGER, OF BROOKLYN, NEW YORK, ASSIGNOR TO RADIO COB- ]?ORATION OF AMERICA, A CORPORATION OF DELAWARE.

INTERFERENCE-REDUCING MEANS FOR RADIO RECEIVING APPARATUS.

Application filed December 18, 1922. Serial No. 607,476.

This invention relates to improved means for combining signals received from the same station at a plurality of receiving stations, and more specifically to means for controlling the space current in a vacuum tube detector or amplifier in accordance with such signals, thus providing means for discriminating between stations located at different places and transmitting on the same wave length.

It-is an object of this invention to provide such means which shall have a sharper tuning characteristic than the means at present used for the purpose, to provide such means in a form which will be simple and inexpensive to build and install and which will be positive and reliable in operation. Still other objects will be apparent from the specification.

My invention is illustrated in the accompanying drawing in which Figure 1 is a diagram illustrating the arrangement of transmitting and receiving stations.

Figure 2 is a diagrammatic view of my invention as applied to two receiving stations.

Figure 3 is a diagram of the results desired.

Figures 4 and 5 are diagrams explaining the operation of my invention.

Referring to Figure 1, A and D represent independent transmitting stations and B and B represent two receiving stations having a common indicating means located at C. It will be understood that the oscillations received at stations B and B may first be amplified if desired and are then transferred by any suitable means to the indicating apparatus at C and there combined to actuate the indicating means. It is well known in the art that signals transmitted from A will, in most cases, be received at stations B and B at different times. This difference in time is, of course, very small but for certain arrangements of the receivingstation with respect to the transmitting stations may cause considerable diiference in phase between the signals arriving at C. It has been suggested to regulate the phase of these signals in order to bring them into phase coincidence, in order to obtain maximum response of the indicating apparatus, and this may in general be accomplished by the use of phase rotators or phase shifting coils which are old in the art.

When apparatus of this type is used, as the signals are brought more nearly into phase they are combined according to the law of cosines, as shown in the dotted line curve of F igure 3. While this arrangement provides a certain amount of geographic selectivity it leaves much to be desired. The ideal arrangement would be required to have a characteristic such as shown by the full line curve 1n Figure 3. This arrangement would give nearly zero response for signals which were out of phase by only a small amount and maximum response only for signals in phase. It is desired that the arrangement be quite sensitive to the amount of phase difference, making it possible to select signals which are different in phase only by a small amount and to reject signals differing by any larger amount. I attain this result by the use of apparatus as shown in Figure 2.

Referring to this figure B and B represent two receiving stations provided with the usual tuning means comprising antennae havlng difierent characteristics with respect to the desired signal, as described in my copending application, Serial No. 607,47 8, filed on December 12, 1924: variable inductances 1 and 1 and variable condensers 2 and 2; a common indicating means such as vacuum tube detector 6 and telephone receiver 7 are provided. The oscillations from stations B and B are impressed upon the grid circuit of the tube in such a manner that they addalgebraically. This is accomplished by providing a coupling transformer 4 whose primary 11 is connected across the inductance 1 and whose secondary 12 is connected in the grid circuit and also acoupling transformer 5 whose primary 13 is connected across the inductance 1 and whose secondary 14 is connected in series with the secondary coupling coil 4:. This constitutes the grid control for the tube 6. The relative phase relationship of the signals may be controlled by means of a phase shifting device, generally designated 10, connected in the line connecting inductance 1 and transformer primary 5. Connected in the plate circuit of the tube 6 I provide the usual indicating means which may be telephone receivers 7, or if desired, the output of this tube may be amplified by one or more amplifiers before actuating the indicating apparatus.

Referring to Figure .5, in operation the grid will be given a comparatively strong negative bias, for instance, as represented by point a by any suitable means such as battery 8 and potentiometer 9. Signals received for instance at station B will not be sufficient to overcome this bias but may increase the grid potential to some point such as b. This is not sufficient to operate the tube. If, however, in addition to the signal from B we now impress also the signal from station B in phase with that from B the grid potential will be carried over to some point C at which the tube willfunction. This is diagrammatically shown in Figure 4 where the dotted line curve represents the potential impressed upon the grid by the incoming signals. It will be seen that this dotted line curve is not the curve which we desire as shown in Figure 3 but is in fact, a small section cut oi the top of the dotted line curve of Figure 3. This would not give suflicient intensity to received oscillations, were it not for the amplifying action of the detector. This amplifying acton, however, increasing the current in accordance with the square law, gives a curve such as shown in full lines in Figure 4. It is obvious that the same result would be obtained by giving the grid a positive bias above the bend in the characteristic of the tube.

It will thus be seen that I have provided means for giving zero response when signals are substantially dephased and at the same time giving maximum response when the signals are subtantially in phase. This may be utilized to advantage in geographic tuning. For instance, referring to Figure 1, if station A is transmitting simultaneously with station D and it is desired to copy from station A the phase rotators or phase shifting coils will be adjusted in such a way that signals from A are brought substantially into phase at C, whereas those from D will be dephased. Thus it Will be possible to copy from station A without interference from station D. In the same manner if it is desired to copy from station D and to eliminate interference from station A the phase shifting coils will be ad justed in such a way that signals from station D will be in phase at C and signals from station A will, therefore, be dephased. It may also be pointed out in this connection that it is not necessary to adjust the phase shifting coils for each station which it is desired to tune out, since a single adjustment to bring into phase the signals from the desired station will, in the nature of things, dephase signals from any other station not in direct line with station A.

I/Vhile I have shown and described the preferred embodiment of my invention it is evident that modifications may be made without departing from the spirit of the same. For instance, I am not limited to only two stations as thismethod and arrangement may obviously be used for as many receiving stations as desired.

Having thus described my invention I declare what I claim is 1. In the reception of radio signals with a plurality of aerials, a common thermionic oscillation-responsive element having a control electrode and means for impressing upon said control electrode oscillations received on said aerials, the method of decreasing interference which consists in maintaining upon such control electrode a bias potential of such mag nitude as to maintain said oscillation-responsive device normally inoperative by an amount slightly less than the sum of signal potentials impressed thereon from each of said aerials when such potentials are all sul stantially in phase.

2. In radio signalling, a method of reception for improving selectivity which consists in receiving desired signalling oscillations at a plurality of geographically separated points, combining such received oscillations substantially in phase coincidence and impressing the combined oscillations on an os cillation-responsive device having a predetermined characteristic while maintaining said oscillation-responsive device in such a condition that substantial phase coincidence of oscillations impressed thereon is required to produce signal potential of sufficient magnitude to yield a response thereof.

3. In radio signalling, a method of reception for improving selectivity which consists in receiving desired signalling oscillations at a plurality of points having different geographical characteristics, combining the oscillations received and impressing the combined oscillations on an oscillation-responsive device having a. predetermined characteristic while maintaining said oscillation-responsive device in such a condition that substantial phase coincidence. of oscillations impressed thereon is required to produce a signal potential of a magnitude suflicient to effect a response thereof.

a. A method of increasing the selectivity of radio receiving systems comprising a plurality of aerials located at geographically separated points and actuating a common oscillation-responsive device by the combined effect of oscillations received upon all of said aerials, which consists in maintaining such oscillation-responsive means in such a condition that it is unresponsive to oscillations impressed thereon except when the combined oscillations reaching said responsive device are in substantial phase coincidence and the algebraic sum of the signal potentials from all said aerials exceeds a fixed predetermined value.

5. A method of increasing the geographical selectivity of a radio receiving system comprising a plurality of geographically spaced energy pick-up devices having a common oscillation-responsive device and means for impression on said oscillation-responsive device oscillations rcceived on each of said energy pick-up devices, which consists in maintaining such oscillation-responsive device in a negatively biased condition such that it is unresponsive to oscillations impressed thereon, except when all of said oscillations are substantially in phase and the algebraically combined signal potentials overcome said negative bias.

6. In radio signalling apparatus, a receiving system comprising two geographically spaced aerial systems, a vacuum tube having its grid circuit coupled to both of said aerial systems, and means for maintaining said tube in a biased condition such that it is unresponsive to receive signal oscillations except when such oscillations are substantially in phase and the combined potentials of the desired signals algebraically added produced a signal potential at least equal to a predetermined intensity.

7. In a radio receiving system, a plurality of geographically spaced antenna members, means associated therewith for selecting a desired signal frequency, a signal detecting device, land lines connecting each of said spaced antenna members with said signal detecting device, and means for biasing said detecting device to a point where the combined in-phase oscillations of said de sired signal received on said antenna members is necessary to produce a signal effect of sutficient intensity to yield a response to said incoming desired signal energy in said detecting device.

8. In a radio signalling apparatus, a receiving system comprising a pair of geographically spaced antennae systems, means associated therewith for selecting a desired signal frequency, a vacuum tube detecting means, means for connecting each of said antenna systems with the input circuit of said detecting tube means for controlling the relative phase of the signal energy from said an- Urattsreaa tenna systems reaching said tube, and means for maintaining said tube in a condition such that it responds to desired received signal oscillations only when said oscillations are substantially in phase and the signal potentials from each antenna system algebraially added in the input circuit of said tube are of an intensity at least equal to a predet rmined value.

9. An arrangement for selectively receiving radio signals comprising, a pair of geographically spaced antenna systems, means associated therewith for selecting a desired frequency, a common receiving device, means for transferring energy from said antenna systems to said receiving device, means for combining the desired received frequency from said antenna. systems substantially in phase coincidence in said receiving device, and means for controlling the sensitivity of said receiving device in a manner such that it responds to the combined desired signal potentials only when said combined desired signals produce signal potentials at least equal to a predetermined intensity.

10. The method of selectively receiving radio signals with a pair of geographically spaced receiving systems each having an antenna and means associated therewith for selecting a desired frequency and a receiving device responsive only to signal efiects of predetermined intensity which consists in selectively receiving signals of the desired frequency at each of said systems, combining the desired received signals substantially in phase coincidence and controlling the sensitivity of said receiving device so that it responds to combined desired signals only when said combined desired signals produce signal effects at least equal to a predetermined intensit RICHARD HOWLAND RANGER. 

